Technique for controlling lost circulation

ABSTRACT

This specification discloses a method of controlling lost circulation in drilling operations. In carrying out the method of the invention, an aqueous mixture of a dispersing agent, an inert particulate material, and a water dispersible oleophilic colloid is introduced into the well. This aqueous mixture is circulated down the well and into the vicinity of a formation into which lost circulation is occurring. The aqueous mixture is then mixed with an oleaginous liquid and a gel is formed which tends to plug the formation into which lost circulation is occurring. The oleophilic colloid may be a normally water swellable clay such as bentonite which has been treated to render it oleophilic. The oleaginous liquid may comprise an oil-base drilling fluid utilized in drilling of the well. The inert material may be a weighting material such as barite.

United States Patent 1 Messenger 11] 3,724,564 [451 Apr. 3, 1973 [21]Appl. No.1v 198,357

[52] U.S. C1 .1 ..175/72, 166/294 [51] Int. Cl. ....E2lb 21/04, E21b33/13, E21b 43/00 [58] Field of Search ....175/72, 70, 65; 166/292, 293,

[56] References Cited UNlTED STATES PATENTS 2,531,812 11/1950 Hauser252/85 2,637,692 5/1953 Nahin ..252/8.5 2,675,353 11/1954 Dawson..252/8.5 2,776,713 l/19S7 'Morgan et al. ..l66/293 2,800,964 7/1957Garrick .'..166/293X 2,990,016 .6/1961 Goins,.1r. et al. .......-166/2933,070,179 12/1962 Moore ..l75/72 3,411,581 11/1968 Alpha ..175/72X3,448,800 6/1969 Parker et a1. ..175/72X 8/1969 Kelly,'Jr. ..l75/72X9/1969 Kelly,Jr. ..l75/72 Primary Examiner-Stephen J. NovosadAttorney-William J. Scherback [57] ABSTRACT This specification disclosesa method of controlling lost circulation in drilling operations. Incarrying out the method of the invention, an aqueous mixture of adispersing agent, an inert particulate material, and a water dispersibleoleophilic colloid is introduced into the well. This aqueous mixture iscirculated down the well and into the vicinity of a formation into whichlost circulationis occurring. The aqueous mixture is then mixed with anoleaginous liquid and a gel is formed which tends to plug the formationinto which lost circulation is occurring. The oleophilic colloid may bea normally water swellable clay such as bentonite which has been treatedto render it oleophilic. The oleaginous liquid may comprise an oil-basedrilling fluid utilized in drilling of the well. The inert material maybe a weighting material such as barite.

9 Claims, 1 Drawing Figure lo 3o OIL PHASIE, VOL.%

l so} 1 so I l l.67t| 321 VOLUME RATIO OF OLEAGINOUS LIQUID AQUEOUSMIXTURE Pmmwma ma 3.724.564

JOSEPH U. MESSENGER INVENTOR Ev /W A954? ATTORNEY BACKGROUND OF THEINVENTION This invention relates to the drilling of wells into theearths crust and more particularly to a new and improved method of lostcirculation control in such drilling operations.

In the drilling of wells into the earth to penetrate subterraneanoil-containing formations, there is commonly employed a drill stringhaving a drill bit connected to the lower end thereof. The drill stringis rotated, thereby rotating the drill bit which penetrates the earth bycutting and breaking the formation whichit contacts. Drilling fluid isconventionally circulated down the drill string and through portsprovided in the drill bit and back to the surface through the annulusformed between the drill string and the wall of the well. Thecirculating drilling fluid performs numerous functions includingremoving the cuttings from the well, cooling the bit, and applyinghydrostatic pressure upon the penetrated formations to control fluidscontained under pressure therein. Drilling muds which may be either oilbase or water base are commonly utilized as drilling fluids. Thesedrilling muds are normally treated to provide desired rheologicalproperties which make them particularly desirable for use in drillingwells. For example, drilling muds may be treated to increase the densitythereof by adding thereto such materials as barium sulfate (barite) andlead sulfide (galena).

One difficulty which is often encountered in drilling operations is lostcirculation which involves the loss of unacceptably large amounts ofdrilling fluid into a formation penetrated by the well. Such a formationis commonly termed a lost circulation zone. Lost circulation may occurwhen the well encounters a formation .of unusually high permeability orone which has naturally occurring fractures or fissures. Also aformation may be fractured by the hydrostatic pressure of the drillingfluid, particularly when a changeover is made to a relatively heavy mudin order to control high formation pressures. Numerous techniques havebeen developed in order to control lost circulation. One commonexpedient is to increase the viscosity of the drilling fluid in order toincrease its resistance to flow into the formation. Another techniqueinvolves the addition of bulk material, such as cottonseed hulls,sawdust, or ground walnut shells, to the drilling fluid. Also, it hasbeen proposed to place a soft plug such as a gel formed by a liquid-claydispersion into the lost circulation zone. For example, as disclosed in.U.S. Pat. No.

2,800,964 to Garrick, a gel may be formed within the well by mixing anaqueous liquid and an oil dispersion of a hydrophilic clay and the gelforced into the lost circulation zone. In another procedure, a hydrauliccement slurry may be placed in the lost circulation zone and allowed toset.

In U.S. Pat. No. 3,467,208, to John Kelly, .lr., there was disclosed amethod of controlling lost circulation in drilling operations. Inaccordance with Kelly, an aqueous suspension of an oleophilic colloidwhich is both water and oil dispersible is introduced into a drillstring which extends into a well. The aqueous suspension is circulatedthrough the drill string and into the wellbore where it is contactedwith an oleaginous liquid to form a gel which tends to plug theformation into which lost circulation occurs.

SUMMARY OF THE INVENTION The present invention is an improvement to theaforementioned U.S. Pat. No. 3,467,208 and to a copending patentapplication, Ser. No. 198,247, entitled METHOD OF CONTROLLING LOSTCIRCU- LATION, by John Kelly, .Ir., filed of even date with the presentapplication. In accordance with the present invention, there is provideda method of alleviating fluid loss into a subterranean formationpenetrated by a well. There is introduced into the well an aqueousmixture of a dispersing agent, an inert particulate material, and awater dispersible oleophilic colloid which acts as an oleaginous gellingagent. This aqueous mixture is circulated down the well and into thevicinity of the formation where it is mixed with an oleaginous liquid,thereby dispersing the oleophilic colloid in the oleaginous liquid andforming a gel. This gel tends to plug the formation and mitigate theloss of fluid thereinto.

I BRIEF DESCRIPTION OF THE DRAWING The drawing is a graph showing theeffect of the inclusion of inert particulate material into an aqueousmixture of dispersing agent and oleophilic colloid when mixed with anoleaginous liquid.

DESCRIPTION OF THE PREFERRED EMBODIMENTS relatively little or no gellingaction in an aqueous liquid.

Particularly suitable for use in the present invention are the normallywater swellable clays which have undergone treatment to render themoleophilic. Exemplary of suitable oleophilic clays are the bentonites orother clays which have been treated with an oil-wetting surfactant suchas a long-chain quaternary or nonquatemary amine. For a more detaileddescription of such clays and the method of preparation, reference ismade to CHEMICAL ENGINEERING, March 1952, pp. 226230; U.S. Pat. No.2,531,812 to I-Iauser; and U.S. Pat. No. 2,675,353 to Dawson, Suitableoleophilic clays also may be prepared by dehydrating a hydrophilic claysuch as bentonite, and then treating the dehydrated clay with a glycolor glycol ether. For a more detailed description of this procedure,reference is made to U.S. Pat. No. 2,637,692 to Nahin. Suitableoleophilic colloids are available under the trade names of Geltone andPetrotone.

The dispersing agent employed :in carrying out the present invention maybe any suitable material which functions to promote and maintainseparation of the individual, extremely fine particles of solids whichare usually of colloidalsize. As will be recognized by those skilled inthe art, various such dispersing agents are conventionally employed indrilling muds in order to maintain adequate dispersion of clays added toimpart desired rheological properties to such muds. Also, as will berecognized by those skilled in the art, certain dispersing agents aremore effective in alkaline environments and therefore it may bedesirable to adjust the pH of the liquid medium into which thedispersing agent is added to an alkaline pH. The pH may be adjusted, forexample, by adding caustic soda to the liquid medium. Examples ofdispersing agents which may be used are lignites, chromelignosulfonates, other lignosulfonates such as iron, nickel, and cobaltlignosulfonates, tannins, and complex phosphates such as polyphosphatesand pyrophosphates. Dispersing agents which have been found to giveparticularly good results when used in accordance with this inventionand which are therefore preferred are chrome lignosulfonates andferrochrome lignosulfonates.

The inert particulate materials employed in carrying out the presentinvention may be any suitable inert particulate materials conventionallyemployed in drilling muds. By inert particulate materials is meantmaterials which are resistant to physical and chemical action.

Such inert particulate materials are particularly resistant to physicalaction such as swelling when contacted by the aqueous and oleaginousliquids employed in carrying out this invention. Examples of inertparticulate materials which may be employed are barium sulfate, commonlycalled barite; lead sulfide, commonly called galena; calcium carbonate;and silica. Of these, barite is preferred because it is more readilyavailable and less expensive.

The present invention is directed to a method of controlling lostcirculation which is primarily applicable when an oil-base drilling mudis employed in the drilling of the wall. In accordance with thisinvention, there is prepared an aqueous mixture of an oleophilic colloidand a dispersing agent, as is described in 'copending application, Ser.No. 198,247, entitled METHOD OF CONTROLLING LOST CIRCULA- TION, by JohnKelly, Jr. Into this aqueous mixture there is added an inert particulatematerial of the type conventionally employed in drilling muds. Theaqueous mixture is pumped down the well where it is mixed with anoleaginous liquid to form a soft plug or gel in the vicinity of theformation into which lost circulation is occurring. This gel then servesto plug the formation and mitigate the loss of fluid thereinto.

The inclusion of inert particulate materials into the aqueous mixtureenables the weight of the aqueous mixture to be tailored to the weightof the drilling mud in the well. This is particularly important when along column of aqueous mixture is employed in a well having fluidcommunication with formations that contain fluids under high pressure.The inert particulate materials in the aqueous mixture occupy spacewhich would otherwise be occupied by the oleophilic colloid.Experimental data later presented shows that the inclusion of inertparticulate material enables a gel having suitable yield strength to beformed with a lesser amount of oleophilic colloid than would otherwisebe required. Also, a lesser amount of oleaginous liquid is required tobe mixed with the aqueous mixture to form a gel. Thus, the inclusion ofinert particulate material facilitates the mixing downhole of theoleaginous liquid with the aqueous mixture in forming a gel.

This invention normally will be used most advantageously in conjunctionwith the drilling procedures employing an oil-base drilling fluid, whichdrilling fluid is pumped downward through the drill string and upward tothe surface of the earth through the annulus. Accordingly, thisinvention is described primarily with reference to such a procedure.

When a lost circulation zone is encountered during drilling, asevidenced for example by a decrease or loss of drilling fluid returnedfrom the well annulus, the introduction of the drilling fluid into thedrill string is temporarily suspended and a slug of an aqueous mixtureof a dispersing agent, oleophilic colloid, and inert particulatematerial is introduced into the drill string.

Thereafter, the drilling fluid is again introduced into the drill stringand an aqueous slug is entrained within the column of drilling fluid andcirculated down the drill string thence into the well through the outletports of the drill hit. As the aqueous mixture enters the well, it ismixed with the oleaginous liquid provided by the oil-base drilling fluidand reacts with this liquid to form a gel.

The aqueous mixture of oleophilic colloid, dispersing agent, and inertparticulate materials is preferably blended at the surface into apumpable slurry. Such a slurry is most readily formed by adding thedispersing agent to the water prior to or concomitantly with theaddition of the oleophilic colloid and inert particulate materialsthereto. Though this step is most desirable when a maximum amount ofoleophilic colloid is to be blended into the aqueous mixture, it isstill desirable when less than this maximum amount of oleophilic colloidis to be employed in the aqueous mixture.

The amount of dispersing agent employed in carrying out this inventionis that amount which will allow a sufficient amount of oleophiliccolloid and inert particulate material to be dispersed in water but lessthan that amount which will reduce the efficiency of the gelling actionwhen the aqueous mixture containing the oleophilic colloid and inertparticulate material is mixed with an oleaginous liquid. The specificamount of any selected dispersing agent to be employed may readily bedetermined by straightforward tests wherein various amounts ofdispersing agent and oleophilic colloids are mixed together to form apumpable slurry which will gel when mixed with an oleaginous liquid. Theamount of oleophilic colloid which should be present in the aqueousmixture is less than that amount which will produce a slurry that is tooviscous to pump and at least equal to that amount which will produceupon mixture with an oleaginous liquid a gel of sufficient strength tomitigate the loss of circulation. The amount of inert particulatematerial which should be present in the aqueous mixture is that amountwherein the ratios of inert particulate material to oleophilic colloidare withinthe range of weight percent inert particulate material to 30weight percent oleophilic colloid and 25 weight percent of inertparticulate material to weight percent oleophilic colloid.

A typical formulation for use in controlling lost circulation isobtained by forming a slurry comprised of the following materials inapproximately the concentrations specified: water 301 grams; oleophiliccolloid of the type available under the trade name of Geltone 200 grams;barite 200 grams; ferrochrome lignosulfonate 2.9 grams; and caustic sodal.6 grams. Such a composition yields a slurry having a density of about1 1.8 pounds per gallon, and which slurry has a Farm apparent viscosityof about 70 centipoises (cps).

Ideally, the drill bit will be located adjacent the lost circulationzone so that as the aqueous mixture and oleaginous liquid are mixed anda gel is formed it is displaced immediately into the lost circulationzone where the gelling action continues until a stiff plug is formed,thus sealing the lost circulation zone. However, in many cases, theprecise depth of the lost circulation zone will be unknown. In suchcases it is important to maintain circulation of the drilling fluid inorder to ensure that the plug that is formed upon mixing of theoleaginous liquid with the aqueous mixture of a dispersing agent, inertparticulate materials, and a water dispersible oleophilic colloid isforced into the lost circulation zone. Due to its thixotropic character,this plug will tend to stiffen after it is displaced into the formationwhere it is subject to lower shear stresses than while circulatingwithin the well.

It is contemplated that in most cases, adequate contact between theaqueous mixture of the dispersing agent, oleophilic colloid, and inertparticulate material and the oleaginous liquid can be obtained simply bypassing the mixture through the outlet ports of the drill bit into thewell. This is particularly true when employing an aqueous mixturecontaining an inert particulate material therein, inasmuch as lessmixing with an oleaginous liquid is required for the formation of asuitable gel. However, if more intimate mixing is desired, the drillstring may be withdrawn from the well and equipped with a mixing subsuch as that described in US. Pat. No. 2,800,964. Thereafter, the drillstring may be reinserted within the well and the aqueous mixtureintroduced as described above.

If desired, a suitable oleaginous liquid, such as the oil-base drillingfluid used during normal operations, may be pumped down the well annulusin conjunction with circulation of the aqueous mixture through the drillstring. These steps should be correlated such that fluid is being pumpedinto the annulus as the aqueous mixture is displaced from the drillstring into the well. This will further promote mixing of the aqueousmixture and the oleaginous liquid and will provide a continuous supplyof oleaginous liquid-to the mixing zone. Desirable yield strengths areexhibited by gels formed by mixing the oleaginous liquid and aqueousmixture of a dispersing agent, inert particulate material, andoleophilic colloid within the range of one volume of oleaginous liquidto three volumes of aqueous mixture and three volumes of oleaginousliquid to one volume of aqueous mixture. Preferably about one volume ofoleaginous liquid is mixed with one volume of aqueous mixture containinga dispersing agent, inert particulate material, and oleophilic colloidto form a gel having a maximum yield strength.

By introducing the aqueous mixture of dispersing agent and oleophiliccolloid into the drill string as a discrete slug, the possibility ofsignificant contact between the oleophilic colloid and the oil-basedrilling fluid within the drill string is substantially reduced. Thus,the tendency of the oleophilic colloid to go into an oleaginousdispersion within the drill string is reduced with the result that thereis little chance of forming a stiff gel within the drill string.

In order to further ensure against the oleophilic colloid within theaqueous mixture contacting the oil-base drilling fluid within the drillstring, the aqueous mixture may be preceded with a liquid buffer systemcomprising an aqueous liquid such as fresh water, brine, or if desired,an aqueous-base drilling fluid having hydrophilic clays dispersedtherein. The buffer system normally will comprise a relatively smallamount, e.g., on the order of one-half to five barrels, depending uponthe depth to the end of the drill string which typically may vary fromabout 1,000 to 25,000 feet. A large amount of liquid buffer systemnormally should be avoided in order to ensure that contact of theaqueous mixture of dispersing agent, oleophilic colloid, and inertparticulate material, and the oil-base drilling fluid will take placeafter the aqueous mixture enters the well from the drill string. Theaqueous buffer liquid should, of course, be substantially free ofoleophilic colloids. A second buffer system identical with thefirstinjected buffer system may be injected into the drill stringimmediately following the aqueous mixture of dispersing agent,oleophilic colloid, and inert particu late materials. This second buffersystem reducesthe possibility of contact within the drill string betweenthe aqueous mixture of oleophilic colloid and the subsequentlyintroduced oil-base drilling fluid.

Results of laboratory tests carried out in accordance with thisinvention are shown in the drawing and following table. The drawing is agraph wherein the volume percent of oleaginous liquid (oil-phase mud) toaqueous mixture of oleophilic colloid employed in forming a gel isrepresentedby the x-axis and the yield strength in pounds per squareinch of the gel so formed is plotted as the y-axis. Also shown along thex-axis is a scale which indicates the volume ratio of oleaginous liquidto aqueous mixture used in forming a gel. The oleophilic colloid used incarrying out these experiments was purchased under the trade name ofGeltone and the inert particulate material was barite. Curve A showsthat a mixture of about 1.67 volumes of oleaginous liquid with 1.0volume of aqueous mixture (no barite) results in the formation of a gelhaving a yield strength of about 5 psi, whereas Curve B shows that amixture of about one volume: each of oleaginous liquid and aqueousmixture (containing about 50 percent Geltone and 50 percent barite)results in the formation of a gel having a yield strength of about 5psi. Curve C shows that mixing one volume of an aqueous mixturecontaining 37.5 percent Geltone and 62.5 percent barite with one volumeof an oleaginous liquid results in the formation of a gel having a yieldstrength of only slightly less than 5 psi and still greater than thatwhich would have resulted if the aqueous mixture had contained no barite(Curve A). Thus, this data shows that adding inert particulate materialto the aqueous mixture lessens the amount of oleaginous liquid requiredto be mixed with the aqueous mixture to form a gel having maximum yieldstrength and, that it is preferred to mix approximately equal volumes ofoleaginous liquid and aqueous mixture in so forming a gel. Further, thisdata shows that preferably the inert particulate material (inparticular, barite) and water dispersible oleophilic colloid shouldbepresent in the aqueous mixture in an amount within the range of weightpercent inert particulate material to 30 weight percent oleophiliccolloid and 25 weight percent inert particulate material to weightpercent oleophilic colloid and still more preferably in an amount ofabout 50 weight percent inert particulate material to 50 weight percentoleophilic colloid.

TABLE Water Oleophilic Bentonite (WOB) Slurry (omposition and PropertiesDensity Fann Apparent Composition of Weight of weight of 1. In thedrilling of a well, the method of alleviating fluid loss into asubterranean formation penetrated by said well comprising:

introducing into said well an aqueous mixture of a dispersing agent, aninert particulate material, and a water dispersible oleophilic colloidwhich acts as an oleaginous gelling agent;

circulating said aqueous mixture down said well and into the vicinity ofsaid formation; and

mixing said aqueous mixture with an oleaginous liquid whereby saidoleophilic colloid is dispersed in said oleaginous liquid and forms agel.

2. The method of claim 1 wherein said inert particulate material isselected from the group consisting of barite, galena, calcium carbonate,and silica.

3. The method of claim 2 wherein said dispersing agent is selected fromthe group consisting of lignites, lignosulfonates, tannins, and complexphosphates.

4. The method of claim 3 wherein said oleophilic colloid is a normallywater swellable clay which has been treated to render it oleophilic.

5. The method of claim 1 wherein said inert particulate material isbarite.

6. The method of claim 5 wherein said barite and water dispersibleoleophilic colloid are present in said aqueous mixture in an amountwithin the range of weight percent barite to 30 weight percentoleophilic colloid and 25 weight percent barite to weight percentoleophilic colloid.

' 7. The method of claim 6 wherein said barite and water dispersibleoleophilic colloid are present in about equal weights in said aqueousmixture.

8. The method of claim 1 wherein said aqueous mixture and saidoleaginous liquid are mixed within the range of one volume of oleaginousliquid to three volumes of aqueous mixture and three volumes ofoleaginous liquid to one volume of aqueous mixture.

9. The method of claim 8 wherein about one volume of said aqueousmixture is mixed with about one volume of said oleaginous liquid.

2. The method of claim 1 wherein said inert particulate material isselected from the group consisting of barite, galena, calcium carbonate,and silica.
 3. The method of claim 2 wherein said dispersing agent isselected from the group consisting of lignites, lignosulfonates,tannins, and complex phosphates.
 4. The method of claim 3 wherein saidoleophilic colloid is a normally water swellable clay which has beentreated to render it oleophilic.
 5. The method of claim 1 wherein saidinert particulate mateRial is barite.
 6. The method of claim 5 whereinsaid barite and water dispersible oleophilic colloid are present in saidaqueous mixture in an amount within the range of 70 weight percentbarite to 30 weight percent oleophilic colloid and 25 weight percentbarite to 75 weight percent oleophilic colloid.
 7. The method of claim 6wherein said barite and water dispersible oleophilic colloid are presentin about equal weights in said aqueous mixture.
 8. The method of claim 1wherein said aqueous mixture and said oleaginous liquid are mixed withinthe range of one volume of oleaginous liquid to three volumes of aqueousmixture and three volumes of oleaginous liquid to one volume of aqueousmixture.
 9. The method of claim 8 wherein about one volume of saidaqueous mixture is mixed with about one volume of said oleaginousliquid.